Sedimentary To Metamorphic

Natural freshwater pearls

Pearl (nacreous calcium carbonate; chiefly aragonite, CaCO₃)

Dark gray rounded river pebble

Likely basalt or fine-grained volcanic rock; exact identification requires testing

Weathered dark stone, possibly basalt

Basalt; commonly plagioclase feldspar, pyroxene, and minor olivine

Painted River Rock

Artificially Coated Sedimentary Rock

Tumbled milky quartz

Quartz (silicon dioxide, SiO₂)

Milky quartz crystal cluster

Quartz (silicon dioxide, SiO₂)

Likely milky quartz

Quartz (silicon dioxide, SiO₂)

Milky quartz

Quartz (silicon dioxide, SiO₂)

Milky quartz

Quartz, silicon dioxide (SiO₂)

Shale or Argillite

Shale (sedimentary) / Argillite (metamorphic)

Rounded gray river cobble

Likely fine-grained sandstone, siltstone, or metamorphosed equivalent; exact identification requires a fresh surface and tests

Amber (likely a small rough amber piece)

Fossilized plant resin; amber is an organic mineraloid, not a crystalline mineral

Anthracite Coal

Anthracite (Carbon-rich Sedimentary-to-Metamorphic Rock)

Quartz-rich pebble

Mostly quartz (SiO₂), possibly a quartzite or vein-quartz fragment

Quartz-bearing granite or pegmatite fragment

Likely granitic material composed mainly of quartz (SiO₂), feldspar, and possibly biotite or hornblende

Dark rounded pebble

Likely basalt or another fine-grained mafic volcanic rock; exact identification is uncertain from the image

Sandstone with Liesegang Rings

Quartzose Sandstone with Iron Oxide Precipitation

Yellow chalcedony or quartz fragment

Microcrystalline quartz, SiO₂ (tentative; possibly iron-stained chalcedony)

Silicified oyster fossil

Fossil oyster shell, commonly Ostrea or Crassostrea, replaced or encrusted by chalcedony/quartz

Quartzite Chert Pebble

Sedimentary Chert / Metamorphic Quartzite (SiO2)

Polished fossil coral

Fossilized coral, commonly agatized coral (silica replacing CaCO₃)

Quartz geode or quartz-bearing rock

Quartz (SiO₂), likely in a chalcedony- or basalt-hosted cavity

Mixed collection of common river stones

Varied lithologies, visibly including quartz-rich rock, dark mafic rock, sandstone, and purple quartz-bearing material

Painted River Rock

Painted Quartzite or Smooth Siltstone

Honey-colored quartz cluster

Quartz, silicon dioxide (SiO₂), likely iron-stained or included quartz

Mixed river stones and gravel

Polymictic alluvial clasts; individual pieces may include quartzite, granite, basalt, sandstone, limestone, and slate

Beach Pebble (Quartzite / Sandstone)

Quartz-rich sedimentary or metamorphic rock pebble

Milky quartz-bearing rock, possibly quartzite

Quartz (SiO₂), likely in a quartzite or quartz-rich vein

Fossilized bone fragment (probable mammalian tooth or bone)

Mineralized bone, commonly hydroxyapatite [Ca5(PO4)3(OH)] replaced or impregnated by silica/calcite

Yellow-orange quartz/chalcedony pebble (possibly citrine-bearing)

Quartz, SiO₂; likely microcrystalline chalcedony with iron staining

Greenschist

Greenschist (composed mainly of chlorite, epidote, actinolite, and albite)

Likely quartz-rich metamorphic rock (quartzite or quartz-veined schist)

Quartzite/siliceous schist; chiefly quartz (SiO₂), with probable mica and iron-oxide staining

Baked-clay ceramic fragment (likely brick or pottery)

Fired clay, primarily aluminosilicate minerals; not a natural rock

Quartz-rich river pebble, likely milky quartz

Milky quartz (SiO₂), possibly a quartzite or quartz-rich silicate pebble

Anthracite Coal

Anthracite (Carbon-based sedimentary-derived metamorphic rock)

K2 Stone

Azurite in Granite

River Pebbles and Quartz

Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)

Weathered fine-grained stone, likely sandstone or quartzite

Quartz-rich sandstone (possibly weakly metamorphosed quartzite); predominantly SiO₂

Rounded gray stone, likely slate or fine-grained sandstone

Probable slate (low-grade metamorphosed shale) or lithic sandstone; exact identification requires testing

Milky Quartz with Iron Inclusions

Quartz (Silicon Dioxide, SiO2)

Small white mineral fragment

Likely quartz (SiO₂), possibly calcite (CaCO₃)

Polished operculum (“Shiva eye” shell)

Calcium-carbonate shell operculum, commonly from a turban snail (family Turbinidae); not a mineral specimen